At the foot of the hill where the ancient Volterra stands lies some of the most extensive halite deposits in Italy. This precious material was subjected to systematic exploitation since the Etruscan epoch, though the first direct testimony dates to the Roman period. Around 980, it appears the Emperor Otto II turned to the master salters of Volterra to start exploiting the halite mines that had been recently discovered in Saxony. Throughout the Middle Ages, the economy of Val di Cecina and of Volterra itself was based on salt extraction. The rights of exploitation of the deposits were at length the object of harsh disputes between the Bishop-Count and the nascent Communal authority. After Florence conquered Volterra (1472), the salt mines were exploited by the Medici family, but it was only with the Lorraines that the extraction assumed an industrial character. Peter Leopold, in particular, stimulated the renewal of the complex. The Grand Duke himself, in 1733, provides one of the most vivid and faithful descriptions of the production structures: «The salterns or salt pans … consist of 5 potholes of salty water from which in 24 hours, hand-operated capstans extract 500 buckets of water, which via certain canals flows into a tank and from here, via other canals, into the 8 boilers where salt is made. These are grouped in the same warehouse and are made of lead; a fire continuously burns beneath them day and night, all year round except for Easter; every 3 hours, wooden rakes are used to pull the salt out of the boiler, and new water is added … Each boiler is staffed by three men … the fires consume 100 loads of wood per day and, around the salt pans, for a distance of 5 miles, extends a reserve of which all wood is destined to serve the salt pans. Every 3 months, the boilers are renewed with lead; a large stone mould is used for the boilers; the lead in pieces is placed on top, and then piles of firewood are heaped on and then set on fire; the lead melts and takes the shape of the boiler. As the salt is removed from the boilers and dried, it is immediately bagged and sent to the warehouses in Volterra». Following the annexation of the Grand Duchy to the Kingdom of Italy, the salterns became Royal property, and later passed under the administration of the State Monopolies (today Atisale). Still today, the commemorative plaques are visible on the little building constructed in Piazza della Salina between 1787 and 1790 by architect Filippo Grobert by order of Grand Duke Leopold II.